Stream events (SSE)

The global event firehose as server-sent events (text/event-stream). Every client consumes this one stream; events are encoded once per update and fanned out per connection, and a slow client is dropped rather than blocking the others. Filter to one session with the sessionId query parameter. Each SSE frame’s id field carries the event id; on reconnect, send it in the Last-Event-ID request header to resume from the first event after it — delivery survives client restarts. Event ids are monotonic integers. The data field of each frame is one JSON Event envelope, discriminated by its type property. A FINISHED TURN’S EVENTS ARE FORGOTTEN. About thirty seconds after a turn ends its events are deleted, and a start of the host deletes each finished turn’s events older than thirty seconds, however recently that turn ended; the transcript is the record of the turn. A replay from a Last-Event-ID below anything this stream has forgotten begins with one replay-gap frame with no SSE id line, so it moves no cursor, followed by the events that remain. A client that receives it re-reads the transcript (listSessionEntries) from what it already holds and resumes the stream from that page’s lastEventId. A REPLAY MAY BE SERVED IN BLOCKS. When the backlog past Last-Event-ID is long, the server writes a bounded block of frames and then ends the connection rather than materialising the whole backlog onto it. The block-end is an ordinary end of connection carrying no marker: a client resumes as it would from any drop, sending the last id it received as Last-Event-ID, and continues from exactly there. Nothing is lost and nothing is duplicated — a client that already skips ids at or below the last one it delivered needs no change at all, and a replay short enough to fit in one block is served exactly as before. A CURSOR THIS STORE CANNOT HONOUR IS REFUSED, not served. A Last-Event-ID naming an event newer than anything the store holds gets 409 (NRY-0026) instead of an open stream: the replay past it is empty by definition and every live event is below it, so a 200 there is a connection that can never carry a frame — silent for the life of the process, with nothing timing out to say so. It is what a client holds after the store underneath it was replaced. A cursor that is merely OLD is unaffected: it replays the events that remain past it, opening with a replay-gap frame when the stream forgot some of them. The remedy is to resume with no Last-Event-ID, never to retry the same cursor.